If you want to take a Puritanical attitude, any luxury item can be argued to be wasteful. Doesn't mean it should be banned. It's up to others to decide how to s

If you want to take a Puritanical attitude, any luxury item can be argued to be wasteful. Doesn't mean it should be banned. It's up to others to decide how to spend their resources. If CO2 emission, and its negative externality, is specifically the problem, then you can advocate that all production of non-essential/luxury items use non-CO2 emitting energy. Unless the measure is agnostic to what category of non-essential activity it targets, you'd just be singling out cryptocurrency, because it's not a non-essential that you personally enjoy spending your resources on.